The invention herein resides in the art of braking systems and, more particularly, to braking systems for aircraft. More specifically, the invention relates to apparatus employed in such braking systems for minimizing the heat buildup within the brake assembly and the transfer of heat among parts, and maximizing the ventilation and cooling of the heat stack. The invention presents a unique heat shield structure, rotor and stator disk configuration, and a flared heat shield, all of which provide for either improved thermal isolation of braking system components or improved thermal dissipation from the heat stack.
Aircraft brakes, whether of steel, carbon, or composite construction, operate on the premise of converting mechanical energy into thermal energy to stop the aircraft upon landing. Such braking operations generally result in the generation of significant heat within the brake disk stack, and the transfer of a significant portion of this heat to other components of the wheel and brake assembly. Those skilled in the art understand that such stacks include a plurality of alternatingly interleaved stator and rotor disks, the former being effectively affixed to the axle of the wheel, and the latter being effectively connected to the wheel itself. Brake actuation devices, such as pistons and return mechanisms, achieve the forceful inter-engagement of rotor and stator disks.
Because of the high temperatures induced in aircraft brake assemblies, heat shields are often used to thermally isolate the heat stack from the wheels, actuator, and other aircraft components. Such heat shields have often included ceramic fibers or other types of insulating materials interposed between the inner and outer heat shield housing layers. However, when brakes are serviced and/or cleaned, cleaning fluids have been found to wick into the insulating materials and to generate significant smoke when subjected to the elevated temperatures encountered during braking operations. Such smoke is obviously undesirable, even if not hazardous. Further, this absorption of fluids by the insulation can also degrade the properties of the insulation.
In prior art aircraft brakes it has also been found that air passages within and about the heat stack are quite restricted. Since it is most desirable to effectuate a cool down of the heat stack in as short a time as possible, it is most desirable that air passageways in and about the heat stack be maximized so that brake cool down can be accelerated and aircraft turnaround time minimized. A specific problem respecting thermal dissipation from the brake heat stack is the lack of adequate annular air space between the brake stack and the wheel. These spaces are constrained by the spacing of adjacent rotor lug faces, rotor and stator outside diameter surfaces, wheel keys and the wheel heat shield. The necessarily compact nature of the brake assembly itself provides little space for the inflow of cool ambient air to these annular spaces. Accordingly, dissipation of heat built up within the brake assembly during a landing/braking operation is delayed by the inability of ambient air to access these areas for the necessary convection.
It has also been well known that heat shields interposed between the brake disk stack and the aircraft wheel and tire have typically been of a uniform cylindrical nature and, while serving to provide an insulating barrier between the brake disk stack and the wheel/tire assembly, the heat shield has not been conducive to enhanced natural convection. In other words, the heat shield has not served to facilitate the passage of air between the cylindrical portion of the heat shield and the brake stack, but has simply been configured for thermal isolation purposes.
There is a need in the art for an aircraft wheel and brake assembly in which the heat shield or shields are so configured as to preclude the wicking of cleaning fluids and the like thereto. There remains a similar need in the art for a heat stack configuration which allows enhanced brake cooling by appropriately configured cooling passages in the lug areas of rotor disks. There also remains in the art the need for heat shields particularly configured to increase the cooling rate of an aircraft brake through enhanced natural convection.
In light of the foregoing, it is a first aspect of the invention to provide an aircraft wheel and brake assembly having a heat shield or shields comprised of one or more sealed pouches.
Another aspect of the invention is the provision of an aircraft wheel and brake assembly in which the heat shield or shields are configured of one or more sealed pouches which contain therein ceramic or other insulating materials.
Still a further aspect of the invention is the provision of an aircraft wheel and brake assembly in which the heat shield pouches are either vacuum sealed or provided with pinhole breathing apertures which minimize thermal expansion, while precluding the wicking of cleaning fluids and the like into the insulating materials.
Yet another aspect of the invention is the provision of an aircraft wheel and brake assembly in which the rotors and stators of the brake disk stack are configured to have apertures in the lugs thereof to accomodate the passage of cooling air.
Still a further aspect of the invention is the provision of an aircraft wheel and brake assembly in which the rotor and stator disks of the brake disk stack are configured with thermal passages in the lugs thereof to provide for enhanced airflow about the periphery of the disks, and in which the disks have increased lug strength as compared to prior art disks employing scallops and the like between the drive keyways.
Yet an additional aspect of the invention is the provision of an aircraft wheel and brake assembly in which the heat shield interposed between the heat stack and wheel/tire assembly of the aircraft includes both a cylindrical portion and a flared end portion accommodating natural convection of ambient air across the brake disk stack.
Yet a further aspect of the invention is the provision of an aircraft wheel and brake assembly having increased thermal efficiency which allows for more rapid turnaround time of aircraft as previously experienced, safer operation and more effective braking than corresponding systems of the prior art.
The foregoing and other aspects of the invention which will become apparent as the detailed description proceeds are achieved by an aircraft wheel and brake assembly, comprising: a wheel mounted upon an axle; a brake assembly interposed between said wheel and said axle; and a heat shield interposed between said wheel and said brake assembly, said heat shield comprising at least one pouch having sealed edges.
Other aspects of the invention are achieved by an aircraft wheel and brake assembly as previously described, and wherein said brake assembly comprises a heat stack of interleaved alternating stator and rotor disks, and wherein said disks have circumferentially spaced lugs separated by keyways, said lugs having air passages therein.
Yet a further aspect of the invention is attained by an aircraft wheel and brake assembly as previously described, and wherein the heat shield comprises a cylindrical portion interposed between the wheel and a brake stack of the brake assembly and a flared portion extending from said cylindrical portion inwardly toward an actuator of said brake assembly.
Additional aspects of the invention are achieved by an aircraft brake disk stack, comprising: a plurality of annular stator disks having uniformly circumferentially spaced lugs about an inner circumference thereof; and a plurality of annular rotor disks interleaved with said stator disks and having uniformly circumferentially spaced lugs about an outer circumference thereof.
Still further aspects of the invention are achieved by an improvement in an aircraft brake assembly having an axle, a hub, a wheel, a brake disk stack, and a brake actuator, the improvement comprising: a heat shield interposed between the wheel and brake disk stack, said heat shield being substantially cylindrical, and having a funnel-shaped mouth at an end thereof.